Feed Hidden Field via JQuery

How do I send a value to a Hidden field via Jquery?

I need to send an array position to it.

Just like any other field:

You can pick up the id:

$(function(){
    $('#id_campo').val(id_array);
});

By name:

$(function(){
    $("[name='nome_campo']").val(id_array);
});

Or by class:

$(function(){
    $(".classe_campo").val(id_array);
});